JPH04122008A - Production method for anisotropic magnet roll - Google Patents

Abstract

PURPOSE:To create a high-quality anisotropic magnet roll by injecting a certain amount of kneaded material through injection openings with a cross-sectional area placed between the magnetic poles around the molded space of a hollow cylinder. CONSTITUTION:A hollow cylinder 3 with a molded space 11 is formed with a non-magnetic, excellent thermal conductor material such as a Be-Cu alloy. Next, a kneaded material which consists of a ferromagnetic powder and a plastic resin is injection molded through the injection openings 10a-10c with a size inversely proportional to the center angle of the metal mold with polarized magnetic materials 21-23. As a result, magnetic flux distribution in the axis direction is uniform and linearity is extremely high. It is also possible to create a high-quality, stable anisotropic magnet roll in which polarization of the axis of easy magnetization is not disrupted.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a magnet roll mainly used as a developing roll in electrophotography, electrostatic recording, etc.

In particular, the present invention relates to a method for manufacturing an anisotropic magnet roll, which includes a step of injection molding a kneaded material mainly consisting of ferromagnetic powder and a thermoplastic resin in a magnetic field.

[Prior Art] Conventionally, in image forming apparatuses such as electrophotographic copying machines, facsimile machines, and printers, magnetic developer is conveyed using
A magnet roll is generally used, in which a permanent magnet member having a plurality of magnetic poles is coaxially inserted into a sleeve made of a non-magnetic material, and the two are rotated relative to each other.

There are various structures for the above-mentioned magnetic rolls, but one example is a long anisotropic roll obtained by press-forming ferrite powder in a magnetic field and then sintering it, as described in Japanese Utility Model Publication No. 57-9798. Some use a permanent magnet member formed by fixing a block magnet around a shaft. Also, those using a permanent magnet member formed by fixing a hollow cylindrical permanent magnet made of hard ferrite to a shaft (for example,
No.-6907.

(See Publication No. 53-47043). However, the former has drawbacks such as a large number of assembly steps and low-temperature demagnetization, while the latter has the presence of magnet material even in the area between the magnetic poles and has a high sintered body density (approximately 5 g
7 cm"), it has disadvantages such as being heavy.

In order to eliminate the above-mentioned drawbacks, a so-called composite magnet is produced by forming a kneaded material mainly consisting of 1 ferromagnetic material powder and a thermoplastic resin into a cylindrical shape by extrusion molding or injection molding, cooling it, solidifying it, and magnetizing it. A magnetic roll using
No. 57-130407. (Refer to Publication No. 57-16450).

When manufacturing these cylindrical composite magnets, a so-called anisotropy process is required to align the axis of easy magnetization of the ferromagnetic material powder with the direction of the lines of magnetic force after magnetization until cooling and solidification is completed. It is well known that there is a
(See Publication No. 96).

When manufacturing the above anisotropic composite magnet by injection molding, the raw material mixture is injected from the nozzle port through the sprue and runner into the molding space of the mold from the injection port, as in the case of general plastics. Molded products are obtained (for example, see JP-A-51-21198 and JP-A-5121199).
. In this case, various injection methods have been proposed in order to uniformly and quickly inject the raw material mixture into the molding space.

[Problem to be solved by the invention]

The anisotropic cylindrical composite magnet that constitutes the above magnet roll has a length/diameter of 5 or more, so it is necessary to uniformly inject the raw material mixture into the hollow cylindrical molding space. Although it is effective to provide an injection port on the outer peripheral surface of the molding space, the above injection means cannot be used in this partial number because a magnetic circuit for generating a magnetic field for imparting anisotropy is installed.

Therefore, an injection port must be provided at the end of the molding space. In this case, a ring-shaped injection port is most effective for uniform injection, but it is difficult to cut near the injection port when releasing the mold, so a method using a multi-point pinpoint injection port is recommended. It is widely used.

However, if the installation position of the injection port is not sufficiently considered, problems such as uneven magnetic flux density distribution when magnetized after molding and so-called magnetic pole twist may occur. In order to eliminate such inconveniences, the applicant has already proposed a method in which the injection ports provided at the ends of the molding space are arranged at positions corresponding to the magnetic poles of the magnetic circuits provided around the molding space. We have made a proposal (see Japanese Patent Laid-Open No. 60-202913).

It has been found that by such a molding method, a molded article with good magnetic properties and no cracks or other defects can be obtained. However, when the magnetic pole positions are arranged at unequal intervals in the circumferential direction.

It has been recognized that while the injected kneaded material moves through the molding space, there is a phenomenon in which it moves in a direction intersecting the axis and crosses over the magnetic pole, which may cause problems such as disordering of the orientation of the T111 easy axis. It was done.

The present invention solves the problems existing in the above-mentioned prior art and provides a method for manufacturing a high-quality anisotropic magnet roll that has a uniform axial magnetic flux density distribution and no disturbance in the orientation of the axis of easy magnetization. With the goal.

(Means for solving problems) In order to achieve the above object, the present invention has the following features.

A kneaded material mainly consisting of ferromagnetic powder and thermoplastic resin is injection molded in a mold that has a hollow cylindrical molding space and a plurality of magnetic poles extending in the axial direction around the molding space. In the method for manufacturing an anisotropic magnet roll, the method includes a step of providing a plurality of injection ports on a circumference substantially concentric with the forming space at an end of the forming space, and connecting these injection ports to the forming space. Placed between the surrounding magnetic poles.

The cross-sectional area of each injection port is set to a value corresponding to the central angle between the magnetic poles, and the kneaded material is injected into the molding space from these injection ports. A technical method was adopted.

In the present invention, the ferromagnetic powder includes ferrite powder having a magnetobrambite crystal structure such as Ba ferrite or Sr ferrite, and 6j! −
Ni-Co magnet powder, Fe-Cr-Co magnet powder,
Known magnet powders such as rare earth cobalt magnet powder and rare earth iron magnet powder can be used.

Further, as the thermoplastic resin which is the binding resin, for example, polyamide resin, polyethylene, ethylene vinyl acetate copolymer, ethylene ethyl acrylate copolymer, polypropylene, etc. can be used.

In addition to the above raw materials, several weight percent of a lubricant such as calcium stearate may be added to improve moldability, and the surface of the ferromagnetic powder may be coated with an organosilicon compound or an organotitanate compound to improve the wettability of the ferromagnetic powder. It can also be pre-processed. It is preferable that the blending amount of the ferromagnetic powder is 2 ferromagnetic powder: thermoplastic resin = 80-94:20-6 (weight ratio), that is, the blending amount of the ferromagnetic powder is less than the above range. and the magnetic properties deteriorate.

On the other hand, if the blending amount exceeds the above range, molding becomes substantially difficult, which is disadvantageous.

Next, if the deviation in the placement position of the injection port or the error in the cross-sectional area is ±20 to 30%, it will not affect the disturbance of the axis of easy magnetization of the molded body.

〔Example〕

FIG. 1 and FIG. 2 are a cross-sectional view and a vertical cross-sectional view of a main part, respectively, showing an example of an injection mold according to an embodiment of the present invention. In both figures, 1 is a sleeve, 1 for example B
The molding space 11 is formed by forming a hollow cylindrical shape from a non-magnetic and thermally conductive material such as an e-Cu alloy. Next, 21 to 23 are magnetic pole members, respectively, which are composed of a permanent magnet (subscript a) with a rectangular cross section and a magnetic pole (subscript b) with a trapezoidal cross section, and each has a central angle of, for example, 70 mm.
° Placed at 90° and 200°. Reference numeral 3 denotes an outer shell material, which is formed into a hollow cylindrical shape from a soft magnetic material such as soft iron, and is attached to the outer periphery of the magnetic pole members 21 to 23. 4 is a spacer, which is made of a non-magnetic material and is made of an outer shell material 3. The gaps between the sleeve l and the magnetic pole members 21 to 23 are filled.

Next, reference numerals 5 and 6 denote an upper lid and a lower lid, which are fitted into the upper and lower ends of the molding space 11, respectively. Note that the upper lid 5 is provided with a nozzle lower, and 2 sprues 8. A runner 9 and an injection port 10 are provided. 12 is a lower stand; 13 is a protruding rod; the shaft 14 is held between the upper lid 5 and the lower stand 12;
In this example, three pieces 10a, 10b, and 10c are provided between the magnetic pole members 21, 22, 22, 23, and 23° 21, and the cross-sectional area of these is set to the center angle 70'' between the magnetic poles.
The angle is set to a size approximately proportional to 90°, 90°, and 200°.

Next, 7.65 kg of Ba ferrite powder with an average particle size of 1 μm
1.35 kg of polyamide resin (nylon 6) was added to the mixture and kneaded in a kneader at 250°C. This kneaded material was injection molded using the mold shown in FIGS. 1 and 2 above.

The injection conditions in this case are injection temperature 270℃, injection pressure 9
00 kg/cs+”, injection time 6 seconds, mold temperature 80℃,
The cooling time was 70 seconds. In addition, permanent magnets 21a and 22a
, 23a contains Br9. Oi+c, +Hc 10
A KOE rare earth permanent magnet (H-22A manufactured by Hitachi Metals) is used, and the outer diameter is 18 m5. A magnet roll material having a length of 260 mm and a shaft outer diameter of 10 m was molded, and after cooling, it was magnetized to obtain a magnet roll. As a comparative example, a magnetic roll similar to the above was manufactured using a mold in which the injection ports 10a, 10b, and 10c shown in FIG. 1 had the same cross-sectional area. The characteristics of these magnetic rolls are shown in the table.

Note (1) Bo: Surface magnetic flux density (on sleeve) (2) ΔB
o: Variation in the axial direction of the magnetic surface skin (on the sleeve) (3) Outer diameter of the permanent magnet member: 1 Bms (4) Outer diameter of the sleeve = 20 - As is clear from the table, 9 according to the method of the present invention Since the twist of the magnetic pole is small, the linearity in the axial direction is extremely good, and it is observed that there is no disturbance in the orientation of the axis of easy magnetization.

In this embodiment, an example in which the permanent magnet member and the shaft are integrally molded has been described, but the effect is similar when a hollow cylindrical permanent magnet member is molded by providing a core in a mold. In addition, although we have described an example in which three magnetic poles are provided in the circumferential direction of the magnet roll, if the number and position of the magnetic pole members arranged in the molding die are changed, the magnetic roll with other numbers of magnetic poles and magnetic pole arrangements can be made. Of course you can get it. Furthermore, as a molding die, not only a permanent magnet type but also a type using a permanent magnet and a pulsed magnetic field, or an electromagnetic type can be used.

From the point of view of downsizing and simplifying the equipment, a permanent magnet type molding mold is most suitable.

[Effect of the invention] Since the present invention has the structure and operation as described above,
The magnetic flux density distribution in the axial direction is uniform, that is, the linearity is extremely good, and there is an effect that a high quality anisotropic mag7notrol without disturbance in the orientation of the axis of easy magnetization can be stably produced.

[Brief explanation of drawings]

FIG. 1 and FIG. 2 are a cross-sectional view and a vertical cross-sectional view of a main part, respectively, showing an example of an injection mold according to an embodiment of the present invention. 10.10a, 10b, 10c: Inlet 11: Molding space, 21, 22.23: Magnetic pole member.

Claims (1)

[Claims] A kneaded material mainly composed of ferromagnetic powder and thermoplastic resin,
A method for manufacturing an anisotropic magnet roll, which includes a step of injection molding in a mold having a hollow cylindrical molding space and a plurality of magnetic poles extending in the axial direction around the molding space. A plurality of injection ports are provided at the end of the space on a circumference substantially concentric with the molding space, and these injection ports are arranged between magnetic poles arranged around the molding space, and each injection port is A method for manufacturing an anisotropic magnet roll, characterized in that the cross-sectional area of the inlet has a value corresponding to the central angle between the magnetic poles, and the kneaded material is injected into the molding space from these injection ports.